1. Field of the Invention
The present invention relates to a technique of producing optical functional fibers having light reflecting and interfering functions.
2. Description of the Related Art
Recently, yarns having deformed cross sections instead of simple round cross section are employed so as to satisfy demands for high-quality textures in fabrics. Further, fibers which appeal to the sensibility of people and can express bulky textures and so on by combining two or more kinds of fibers have been developed. However, demands for fabric textures are becoming more and more critical recently, and fabrics having higher expressiveness and facilities are now on demand. What decides texture of a fabric includes color depth and luster. However, it is extremely difficult for fibers to satisfy both color depth and luster simultaneously. More specifically, if one tries to obtain a fiber having a deep color, an unvivid dull-colored fiber is resulted, whereas if one tries to obtain a lustrous fiber, a gaudy glittery fiber is resulted. Accordingly, there is developed so far no technique for producing fibers filly satisfying both color depth and luster.
The reason is that dyes or pigments have conventionally been employed for developing color depth and luster. In this case, since dyes and pigments develop colors based on light absorption, the deeper is the color one tries to obtain, the smaller becomes the reflected light, and luster is lost. On the other hand, the more lustrous is a fiber one tries to obtain, the smaller becomes the light to be absorbed, and color depth is lost.
In view of the problems described above, there is recently proposed a technique for producing fibers having color depth and luster without resorting to dyes and pigments. This technique employs as the color-developing mechanism reflection and coherence of light instead of light absorption as employed in the cases where dyes or pigments are used. Synthetic fibers utilizing this mechanism are also under development.
For example, Japanese Patent Publication No. Sho 43-14185 discloses a coated three-layer composite fiber having pearl effect. However, such fibers having merely some three layers may develop colors based on light reflection and coherence, but the degree of color development is too limited to be able to satisfy the demands for higher expressiveness or sensibility.
Meanwhile, Japanese Patent Publication No. Sho 60-1048 discloses a technique for obtaining a synthetic fiber, in which different kinds of polymers are combined alternately and repeatedly in a spinning pack equipped with a stationary mixer, and the resulting polymer is injected through injection orifices. In this official gazette, there is disclosed a composite fiber consisting of polyethylene terephthalate and nylon 6 formed by layering them via a multilayered film component employing a stationery mixer. This fiber is a multilayered fiber in which the layer interfaces are substantially parallel to one another, and thus the fiber can give textiles having pearl effect. However, in this method, layer flows are disturbed little by little each time two polymers are combined with each other. Although multiple layers can be obtained somehow, they are of such a degree of optical accuracy that it can give sufficient coherence of light, and it is difficult to control the thickness of each layer. Particularly, when a multilayered structure having 10 or more layers is to be formed, fibers must be combined several times or more, so that the layers are liable to have irregular thickness giving coherent beams of light having insufficient intensity and that coherent beams of light having various wavelengths, i.e. turbidity in color, are observed, resulting in the failure of obtaining colors having satisfactory expressiveness or sensibility.
Further, Japanese Patent Publication No. Sho 57-20842 describes a static fluid mixer; and Japanese Patent Publication Nos. Sho 53-8806 and Sho 53-8807 describe methods of spinning blended yarns and the like. According to these methods, fibers are obtained by combining two kinds of polymers and separating them repeatedly, so that they can give no multilayered fiber having sufficient optical accuracy due to complication of the polymer flows,
Further, Japanese Unexamined Patent Publication Nos. Sho 62-170510 and Hei 4-202805 disclose methods for obtaining coherent beams of light by forming fine unevenness on the fiber surface. According to these methods, coherence of light is induced by forming a diffraction grating on the fiber. However, it is true that such fibers show color development based on coherence of light, but wavelength of coherent beams of light in fabrics woven by them vary easily depending on the angle of view. Accordingly, in this case, the colors of the fabrics vary only to give cheap expressiveness.
Meanwhile, Japanese Unexamined Patent Publication No. Sho 59-228042, Japanese Patent Publication Nos. Sho 60-24847 and Sho 63-64535, etc. propose color developing fibers and fabrics developed taking a hint from the morpho butterflies in South America which is famous for their variable color tone depending on the angle of view and bright color effect. However, the fibers employed in the inventions described in the above official gazettes are flat yams formed by laminating different kinds of polymers together, so that it is almost impossible to obtain a thickness so as to induce coherence of light, and such structures merely serve to control reflection of light.
Meanwhile, a multi-ply lamination fiber compound of different kinds of polymers is disclosed in Japanese Unexamined Patent Publication No. Sho 54-42421. However, in the method described in this official gazette, the laminated portion is allowed to assume an annular form, and one component in the laminated portion is melted to obtain a superfine fiber. Accordingly, such fibers cannot exhibit the effect of coherence.
Further, Japanese Unexamined Patent Publication Nos. Hei 7-34320, Hei 7-195603 and Hei 7-331532 each propose a technique for obtaining a fiber which is not dyed and yet can develop color and which also has ultraviolet and infrared radiation fleeting function by layering alternately two kinds of polymers having different refractive indices and adjusting the optical thickness of each layer.
Meanwhile, there is also published a technique for obtaining a material which shows color development by employing a sandwich structure of a molecule-oriented anisotropic film between polarizing films (e.g., Journal of Textile Machinery Society, Vol. 42, No. 2, p.55 (1989), and Vol. 42, No. 10, p.160 (1989), ibid.).
Further, Japanese Unexamined Patent Publication Nos. Hei 7-97766 and Hei 7-97786 disclose fiber fabrics each having on the surface a light interference film provided with a substantially transparent thin film layer which can develop color with the aid of the reflected light of incident light from the front surface and the light reflected by the rear surface. Wavelength of coherent beams of light resorting to such thin films varies depending on the angle of view, so that the color of the fabric changes depending on the angle of view, only to give here again cheap expressiveness as described above.
The present invention is directed to overcome the problems described above and to provide a technique for producing a fiber which develops a single color having both color depth and luster sufficiently.